In order to improve design or decorative property or excellent touch or texture (e.g., soft texture), or in order to impart higher functionalities, there have been proposed composites (molded composite articles) formed with a combination of a plurality of resins each having a different hardness, for example, a molded composite article in which at least a part of a resin molded article is coated with a thermoplastic elastomer. Such a molded composite article is usually produced by adhesion of a plurality of molded members through an adhesive. For example, Japanese Patent Application Laid-Open No. 267585/1996 (JP-8-267585A) (Patent document 1) discloses a resin molded article in which a plurality of resin molded articles formed with a polyamide resin or others are weld or adhered to each other through a finishing agent such as a urethane polymer or a urethane-series adhesive. However, such a process using an adhesive is not only uneconomical due to complicated steps, but also has problems such as environmental pollution by an organic solvent or others. Furthermore, in the case where such a resin molded article is small in adhesive area or needs (or requires) fine patterns, production of such a resin molded article on a commercial or industrial basis is difficult because not only a coating step of an adhesive becomes quite complicated, but also bonded strength or bonded stability of the resin molded article is insufficient.
On the other hand, from the viewpoint of rationalization of production processes or environmental protection, a process for direct thermal fusing of a plurality of molded members has been adopted. The molded composite article obtained by thermal fusing is usually manufactured by a molding process such as a two-color (or double) molding or an insert molding. However, combination of materials which are different in species and are acceptable for thermal fusing is significantly limited, and in many cases the combination is only limited to the same kind of materials. Moreover, it is not easy to establish molding conditions for obtaining enough bonded strength. Therefore, in order to reinforce the fused part, such a method is utilized in addition to thermal fusing or welding, that a method for preparing a concavo-convex site (or part) in an area to be bonded of the molded member for mechanical joining, a method for chemically activating a surface of the molded member by a corona discharge treatment or the like, a method for coating a primer or others on an area to be bonded, or other methods. In such a method, however, the molded composite article is deteriorated in flexuous property. For example, the hardened primer layer easily forms a crack with bending. Moreover, the method tends to require a complicated structure of the molded member, or increases the number of production steps. As a result, such a method has many disadvantages in quality of product and economic circumstances.
In order to solve these problems, it has been investigated to use a thermoplastic polyurethane as a material for a resin member constituting a molded composite article. The thermoplastic polyurethane itself is relatively excellent in adhesiveness. For example, in a usage (or purpose) of shoe(s), a molded composite plastic article comprising a polyamide resin and a thermoplastic polyurethane is practically used as a shoe sole. For example, Japanese Patent Application Laid-Open No. 248201/1997 (JP-9-248201A) (Patent document 2) proposes a centroid body for a cycling shoe, which comprises a shoe sole member formed with a polyamide resin reinforced with a glass fiber as an insert, wherein a sidewall of the shoe sole member is molded with a polyurethane resin. However, since such a usage exposes the centroid body to a mechanically severe condition, the reference describes in Examples, that a through-hole in the polyamide resin shoe sole member is needed for mechanical conjunction of the sole member with the polyurethane resinous sidewall member. Moreover, Japanese Patent Application Laid-Open No. 308205/1995 (JP-7-308205A) (Patent document 3) proposes a shoe sole reinforced by replacing at least a part of the outsole composed of a polyurethane resin with a fiber reinforced polyamide resin sheet. This reference discloses that the polyamide resin comprises a mixture of a polyamide and a polyolefin (an ionomer) in order to obtain bonding or joining properties tolerant to heavy bending of the shoe sole. As apparent from these references, for the usage of shoe soles and others which require excellent mechanical properties or bending or flexing fatigue resistance, it has been watched to combine a thermoplastic polyurethane resin excellent in bonding properties by itself and a polyamide resin surpassing in mechanical properties. In general, since a thermoplastic polyurethane-series resin itself has a bondability to a polyamide-series resin to a certain degree, in adequate conditions such as material temperature in bonding or others, a molded composite article is obtainable which has a bonded strength durable to the practical use. However, in the case where high bending or flexing fatigue resistance is required to the bonded surface, or where using environment of bonded member is extremely severe, much higher (one-step higher) bonded strength than the above molded composite article is required. That is, bondability (strength) of members obtained by thermal fusing or welding is insufficient, and further ingenuity or improvement is necessary.
Among the field of these shoe soles, in the field of athletic shoe such as a succor, baseball, or basketball shoe, in order to obtain higher flexibility as a shoe sole as well as strong bondability between materials, there is widely employed a molded composite article combining a polyurethane resin and a polyamide-series elastomer having not only high flexibility and toughness but also excellent bondability (that is, an elastomer in which a polyamide-series resin is softened by introduction of a polyether component).
For example, Japanese Patent Application Laid-Open No. 505333/1996 (JP-8-505333A) (Patent document 4) discloses that a lightened shoe sole is obtained by injection-molding a polyamide elastomer containing a foaming agent into a mold, with inserting or putting a molded article of a thermoplastic resin such as a polyether amide, a polyether ester or a polyurethane in a mold, and adhering to the thermoplastic resin molded article (un-lightweight (un-lightened) plastic) and the elastomer (lightweight thermoplastic elastomer). Japanese Patent Application Laid-Open No. 125155/1995 (JP-7-125155A) (Patent document 5) discloses a molded composite article in which a rigid plastic molded member formed of a blended matter of a polypropylene and a polyamide is coated with a non-rigid (or flexible) plastic containing a thermoplastic polyurethane and a plasticizer by thermal fusing. However, even in such a molded composite article (for example, a molded composite article using a polyurethane resin), the adhesive strength between two materials (e.g., an adhesive strength relative to a polyamide elastomer as a counterpart member) has not been enough yet. Therefore, such a composite is affected by not only conditions for molding or conditions of materials to be used (e.g., production lot) but also using environment of the product (molded composite article), resulting in unstableness of the bonded strength or the duration of the molded composite article (particularly the duration of the adhered site).
Among the combinations of a polyurethane resin and a polyamide-series elastomer, in both practical use in market and the examples of the Patent Document 4, a polyether-series polyurethane resin is used as the polyurethane resin, and as a matter of fact, the composite comprising a polyester-series polyurethane resin and a polyamide-series elastomer is not produced. However, the polyester-series polyurethane resin is excellent in mechanical properties and economical efficiency than the polyether-series polyurethane resin. Therefore, not limited to the market of an athletic shoe, in all the field utilizing a composite of a polyurethane-series resin and a polyamide-series resin, it is a great issue in terms of both technical and commercial subjects that both polyether-series polyurethane resin and a polyester-series polyurethane resins are used with no distinction in technology development for a composite.
Further, Japanese Patent Application Laid-Open No. 273826/2002 (JP-2002-273826A) (Patent document 6) discloses a composite comprising a combination of a vulcanized rubber member in which a rubber is vulcanized with a radical-generating agent and a resin member comprising a thermoplastic resin having at least two hydrogen or sulfur atoms per molecule on average, wherein the hydrogen or sulfur atom has an orbital interaction energy coefficient S of not less than 0.006. However, this method needs compulsory contact both members with each other with heating both members (usually at a temperature of not less than 160° C.) for a given length of time (usually not less than 7 minutes) due to necessity of a crosslinking agent for binding both members. Therefore, in fact, in some final product configurations of the composite, this method is unusable for a material having low heat-resistance, particularly the material having a deflection temperature of not more than 100° C. under a load of 0.45 MPa defined by ISO 175. Moreover, in the case of using a material having relatively a high heat-resistance, it is difficult to obtain a molded composite article having a high dimensional accuracy because the exposure to the condition of a high temperature and a high pressure for a long period inevitably causes physical developments such as expansion and contraction in the molded composite article.    Patent Document 1: JP-8-267585A (Claims)    Patent Document 2: JP-9-248201A    Patent Document 3: JP-7-308205A    Patent Document 4: JP-8-50533A    Patent Document 5: JP-7-125155A (Claims)    Patent Document 6: JP-2002-273826A